1. Field of the Invention
Exemplary embodiments of the invention relate to a light emitting diode and, more particularly, to a light emitting diode having electrode pads.
2. Description of the Background
Gallium nitride (GaN) based light emitting diodes (LEDs) have been used in a wide range of applications including full color LED displays, LED traffic signals, and white LEDs.
The GaN-based light emitting diode may be generally formed by growing epitaxial layers on a substrate, for example, a sapphire substrate, and includes an N-type semiconductor layer, a P-type semiconductor layer, and an active layer disposed between the N-type semiconductor layer and the P-type semiconductor layer. Further, an N electrode pad is formed on the N-type semiconductor layer and a P electrode pad is formed on the P-type semiconductor layer. The light emitting diode is electrically connected to and operated by an external power source through these electrode pads. Here, electric current is directed from the P-electrode pad to the N-electrode pad through the semiconductor layers.
Generally, since the P-type semiconductor layer may have a high resistivity, electric current may not be evenly distributed within the P-type semiconductor layer, but may be concentrated on a portion of the P-type semiconductor layer where the P-electrode pad is formed. Electric current may be concentrated on and flow through edges of the semiconductor layers. This may be referred to as current crowding, and may lead to a reduction in light emitting area, thereby deteriorating luminous efficacy of a source. A transparent electrode layer having a low resistivity may be formed on the P-type semiconductor layer to enhance current spreading. In this structure, electric current supplied from the P-electrode pad may be dispersed by the transparent electrode layer before entering the P-type semiconductor layer, thereby increasing a light emitting area of the LED.
However, since the transparent electrode layer may tend to absorb light, the thickness of the transparent electrode layer is limited, thereby providing limited current spreading. In particular, for a large LED having an area of about 1 mm2 or more, there is a limitation on current spreading through the transparent electrode layer.
To facilitate current spreading within a LED, extensions extending from the electrode pads may be used. For example, U.S. Pat. No. 6,650,018 discloses an LED that includes a plurality of extensions extending in opposite directions from electrode pads to enhance current spreading. Although the use of extensions may enhance current spreading over a wide region of the LED, current crowding may still occur at portions of the LEDs where the electrode pads are formed.
Moreover, as the size of the LED increases, the likelihood of a defect being present in the light emitting diode may increase. Defects such as threading dislocations, pin-holes, etc. provide a path through which electric current may flow rapidly, thereby disturbing uniform current spreading in the LED.